1. Field of the Invention
The present invention relates to a saturable reactor having a magnetic switching function which serves to switch between a high inductance state and a low inductance state and a low-inductance conductive function in accordance with the direction of the current flowing therethrough so as to perform high-speed, large-power rectification. It further relates to a power source apparatus for pulse laser utilising the saturable reactor.
2. Description of the Related Art
Saturable reactors comprising a magnetic core of ferrite or amorphous magnetic material have conventionally been used as magnetic switches by utilising the non-linear permeability of the magnetic material. The configuration of these saturable reactors is such that a principal coil is wound a prescribed number of times around the magnetic core. When the electric current I flowing through the principal coil increases, so does the magnetic flux density B as illustrated in FIG. 5. Once the magnetic flux density B reaches B0, the magnetic core becomes a state of saturation in which the constant magnetic flux density B0 is maintained despite a further increase in the electric current. In this state of saturation, the inductance of the magnetic core is very small. As a result, the saturable reactor fulfils the function of a magnetic switch. Even if the electric current flows through the principal coil in the opposite direction, it still fulfils the same magnetic switching function. The absolute value of the electric current at which the transition from unsaturated to saturated state occurs is the same, as is the magnetic flux density, and the B-H characteristics are in point symmetry with respect to the origin.
Japanese Patent Publication 62-76511 proposes an improved saturable reactor in which a supplementary coil is wound around a saturable iron core in addition to a principal coil. By feeding a bias current to the supplementary coil in accordance with the current in the principal coil, a magnetic switch is provided which performs controllable switching action for the electric current flowing through the principal coil. With this satiable reactor, by altering the amount of current in the supplementary coil, it is possible to switch with the desired timing without regard to the amount of current flowing through the principal coil.
However, conventional saturable reactors with a supplementary coil such as the magnetic switch described in Japanese Patent Publication 62-76511 has the supplementary coil for the purpose of resetting the magnetism.
For instance, in the power source apparatus for pulse laser illustrated in FIG. 6, electric charge is stored directly into a capacitor C11 by a charger 11 which forms a power source for charging. The electric charge stored in this capacitor C11 begins transferring energy when a switch SW1 turns on. More particularly, as the switch SW1 turns on, the voltage generated across a saturable reactor SL11 increases, and after a predetermined assist time at that voltage, that is, after a product of time and voltage reaches a predetermined value, the saturable reactor SL11 reaches saturation, turning the saturable reactor SL11 on. The electric charge stored in the capacitor C11 is transferred in the form of the current I11 by way of the saturable reactor SL11 and the switch SW1 to the opposite side of the capacitor C11. Thereafter, voltage is generated across the saturable reactor SL12, turning it on when the saturable reactor SL12 reaches saturation after a predetermined assist time at that voltage. The electric charge stored in the capacitor C11 is transferred in the form of the current I12 to a peaking capacitor CP1. The electric charge which has been transferred to the peaking capacitor CP1 becomes the electric current I13, which causes the laser discharge unit LD1 to discharge, creating laser pulse oscillation.
However, in the power source apparatus for pulse laser illustrated in FIG. 6, when the switch SW1 turns on and the electric charge which has been charged in the capacitor C11 is transferred, this causes the voltage P0 across the capacitor C11, which has been positive during charging, to reverse polarity and rapidly change into negative. From the point at which the voltage P0 becomes negative, the electric current I01 is output from the charger 11. As a result, it sometimes happens that the charging current flowing out from the charger 11 increases beyond its design value, leading to problems of damage to the charger 11 and inferior accuracy of charging.
Meanwhile, in the power source apparatus for pulse laser illustrated in FIG. 7, a charger 12 charges at least a capacitor C12 by way of a saturable reactor SL21. When a switch SW2 turns on, voltage is generated across the saturable reactor SL21. When the saturable reactor SL21 turns on after a product of time and voltage reaches a predetermined value, electric charge stored in the capacitor C12 in the form of current 121 is subjected to a reversal of polarity whereby it is transferred to the opposite side of the capacitor C12. Thereafter, voltage is generated across a saturable reactor SL22, turning it on after a predetermined assist time at that voltage. The electric charge transferred to the, capacitor C12 in the form of current 122 is transferred to the peaking capacitor CP2. The electric charge which has been transferred to a peaking capacitor CP2 becomes electric current 123, which causes a laser discharge unit LD2 to discharge, creating laser pulse oscillation.
However, if there are ripples in the electric current flowing from the charger 12 in the power source apparatus for pulse laser illustrated in FIG. 7, when the charger 12 charges the capacitor C12 by way of the saturable reactor SL21, the frequency of these ripples causes the inductance of the saturable reactor SL21 to increase, inhibiting the charging of the capacitor C12, with the result that a surge voltage is generated at point P1 on the charger 12 side of the saturable reactor SL21. This surge voltage is problematic in that it may exceed the withstand voltage of the switch SW2 and cause it to break, while it also makes it impossible to detect the voltage across the capacitor C11 with accuracy.
In such a case, if the saturable reactor SL21 is conductive in the direction of the charging current and has the magnetic switching function for the magnetic compression action of the charged electric charge, the switch SW2 can be protected because surge voltage is not generated, and also the electric current with ripples can be utilised as the charging current.
It is an object of the present invention to eliminate such problems as described above, and to provide a saturable reactor having a conductive state and a magnetic switching function corresponding to the direction of the electric current, and a power source apparatus for pulse laser utilising the satiable reactor.
The first aspect of the present invention is a saturable reactor comprising a saturable magnetic core; a principal coil wound around the saturable magnetic core; a subsidiary coil wound around the saturable magnetic core; and a power source which feeds electric current to the subsidiary coil when the transition of the saturable magnetic core from unsaturated state to saturated state is effected by the subsidiary coil, characterised in that the saturable magnetic core becomes saturated state immediately when voltage is applied to the principal magnetic coil in the same direction as the current in the subsidiary magnetic coil, while becoming the saturated state from an initial unsaturated state at the time when a product of the voltage and time reaches a predetermined value if the voltage is applied to the principal magnetic coil in a direction opposite to the current flowing in the subsidiary magnetic coil.
In the first aspect of the invention, the current fed to the subsidiary coil is set to exactly the level at which the transition from unsaturated to saturated state occurs in the saturable magnetic coil. As a result, if voltage is applied to the principal coil in the direction which causes magnetic flux to be generated in the same direction as that of the magnetic flux which is generated by the electric current flowing in the subsidiary coil, the state of saturation is maintained and the principal coil becomes a state of low inductance, which is to say a conductive state. Meanwhile, if voltage is applied to the principal coil in the direction of cancelling the magnetic flux which is generated by the electric current flowing in the subsidiary coil by the magnetic flux to be generated by the principal coil, a transition from the initial unsaturated state or state of high inductance to a state of saturation or low inductance occurs when the product of voltage and time reaches a prescribed value. With this configuration, the saturable reactor takes a conductive state and has a magnetic switching function according to the direction in which the electric current flows through the principal coil. In other words, it results in the production of a rectifying element wherein the switching function of a saturable reactor is displayed in one direction of flow of electric current through the principal coil, while conductive state is displayed in the other direction.
Because the saturable reactor of the present invention is a high-speed device that is able to withstand high levels of electric power and high voltage in particular, it can be used in the high voltage levels which semiconductor power devices are incapable of withstanding.
The second aspect of the present invention is a power source apparatus for pulse laser comprising a direct-current power supply for charging; a switch element connected in parallel to the direct-current power supply; a magnetic pulse compression circuit comprising a serially connected saturable reactor and capacitor connected in parallel to the switch element; another one or a plurality of serially connected saturable reactor and capacitor successively connected in parallel to the parallelly connected capacitor in proceeding stage so that when the switch element turns on, the energy stored in the capacitors is transferred successively to the capacitor of next stage; and a laser discharge unit connected in parallel to the capacitor in final stage, wherein charging current from the direct-current power supply flows through the saturable reactors, and the saturable reactors comprises a saturable magnetic core; a principal coil wound around the saturable magnetic core; a subsidiary coil wound around the saturable magnetic core; and a power source which feeds electric current to the subsidiary coil when the transition of the saturable magnetic core from unsaturated state to saturated state is effected by the subsidiary coil, wherein the saturable magnetic core becomes saturated state immediately when voltage is applied to the principal magnetic coil in the same direction as the current in the subsidiary magnetic coil, while becoming the saturated state from an initial unsaturated state at the time when a product of the voltage and time reaches a predetermined value if the voltage is applied to the principal magnetic coil in a direction opposite to the current flowing in the subsidiary magnetic coil.
The second aspect of this invention applies the saturable reactor of the first aspect of the invention to the saturable reactor of the first stage in a power source apparatus for pulse laser. Not only does this result in a pulse compression process utilising the saturable reactor, but when electric charge is stored in the capacitor of the first stage by way of the saturable reactor of the first stage, also makes it possible to avoid the occurrence of surge voltage on the side of the saturable reactor nearest to the direct-current power source for charging, thus preventing breakage to the switch element as a result of that surge voltage.
The third aspect of the present invention is a power source apparatus for pulse laser the same as the second aspect of the invention, wherein the saturable reactors other than the saturable reactor of the final stage in the magnetic pulse compression circuit are same as the saturable reactor of the first stage in the magnetic pulse compression circuit.
This configuration displays the same function and effect as the second aspect of the invention.
The fourth aspect of the present invention is a power source apparatus for pulse laser in the second and third aspects of the invention, further comprising a diode which is connected serially to the saturable reactor the final stage of the magnetic pulse compression circuit, conductive direction of the diode being energy transfer direction by the magnetic pulse compression circuit.
With this configuration, it is possible not only to reduce the voltage applied to the laser discharge unit during charging, thus eliminating unnecessary discharge at that stage, but also to return to the capacitor of the preceding stage any energy which remains after being fed to the laser discharge unit, which greatly improves the efficiency of energy consumption at the next pulse oscillation.